The present invention relates to powertrain mounts for motor vehicles, and more particularly to a powertrain mount having a variable orifice track.
It is desirable to provide motor vehicles with improved operating smoothness by damping and/or isolating powertrain vibrations of the vehicle. A variety of mount assemblies are presently available to inhibit such engine and transmission vibrations. Hydraulic mount assemblies of this type typically include a reinforced, hollow rubber body that is closed by a resilient diaphragm so as to form a cavity. This cavity is separated into two chambers by a plate. A first or primary chamber is formed between the partition plate and the body, and a secondary chamber is formed between the plate and the diaphragm.
The chambers may be in fluid communication through a relatively large central passage in the plate, and a decoupler may be positioned in the central passage of the plate to reciprocate in response to the vibrations. The decoupler movement alone accommodates small volume changes in the two chambers. When, for example, the decoupler moves in a direction toward the diaphragm, the volume of the portion of the decoupler cavity in the primary chamber increases and the volume of the portion in the secondary chamber correspondingly decreases, and vice-versa. In this way, for certain small vibratory amplitudes and generally higher frequencies, fluid flow between the chambers is substantially avoided and undesirable hydraulic damping is eliminated. In effect, the decoupler is a passive tuning device.
As an alternative or in addition to the relatively large central passage, an orifice track is normally provided. The orifice track has a relatively small, restricted flow passage extending around the perimeter of the orifice plate. Each end of the track has an opening, with one opening communicating with the primary chamber and the other with the secondary chamber. The orifice track provides the hydraulic mount assembly with another passive tuning component, and when combined with the decoupler, provides at least three distinct dynamic operating modes. The particular operating mode is primarily determined by the flow of fluid between the two chambers.
More specifically, small amplitude vibrating input, such as from relatively smooth engine idling or the like, produces no damping due to the action of the decoupler, as explained above. In contrast, large amplitude vibrating inputs, such as large suspension inputs, produce high velocity fluid flow through the orifice track, and an accordingly high level of damping force and desirable control and smoothing action. A third or intermediate operational mode of the mount occurs during medium amplitude inputs experienced in normal driving and resulting in lower velocity fluid flow through the orifice track. In response to the decoupler switching from movement in one direction to another in each of the modes, a limited amount of fluid can bypass the orifice track by moving around the edges of the decoupler, smoothing the transition.
The present invention is a powertrain mount comprising an orifice plate and a track member. The orifice plate has an exit, a first surface sloping toward the exit, and an inner surface. The track member has an outer surface proximate the first surface of the orifice plate, and the outer surface of the track member has an entrance. A containment plate forms an orifice track with the first and inner surfaces of the orifice plate and with the outer surface of the track member.
Accordingly, it is an object of the present invention to provide an improved powertrain mount of the type described above that reduces the dynamic stiffness of the mount at a disturbance frequency.
Another object of the present invention is to provide an improved powertrain mount of the type described above in which the orifice track length and area are variable.
Still another object of the present invention is to provide an improved powertrain mount of the type described above in which the orifice track length and cross-sectional area change as a function of the disturbance frequency.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.